A straight engine swap for the 2013 Mercedes CLS63 AMG?

That's right. Both models still use the 5.5-litre bi-turbo V8, but power in the regular CLS63 now sits at 549bhp, while the S-model gets boosted to 577bhp. Previously the CLS63 saloon boasted 517bhp, or 549bhp with the optional AMG Performance Pack.

The Shooting Brake was only available with the uprated engine from launch, thanks to UK buyers rarely speccing the 'slower' car. In for a penny...

As is the Germanic norm, all models are limited to a top speed of 155mph, and the lower-powered car hits 62mph in 4.2sec. Mercedes hasn't released a figure for the faster S-model. Why not? Well, it's because we'll get it in rear-drive form only, and Mercedes has only quoted 0-62mph figures for the all-wheel drive 4Matic version reserved for our continental cousins.

Incidentally, the all-paw CLS63 will hit 62mph in 3.6 seconds, despite its 70kg weight penalty thanks to the traction afforded by the extra driveshafts.

Why don't we get the 4x4 CLS63 AMG in the UK?

It's simply a question of customer demand, rather than right-hand drive conversion issues. Mercedes says it can't justify selling its 4Matic range here, which stretches from humdrum C-class and E-class models to the flagship AMG cars.

Perhaps when the A45 AMG and CLA45 AMG arrive later in 2013 (both sporting 4Matic as standard) those attitudes will change.

Any other CLS63 AMG changes for 2013?

It's all carried straight over from the E63 stablemate. Adaptive suspension is standard, as is the four-mode seven-speed DCT paddle-shift transmission. The model range changes will come into effect in April 2013, with the 577bhp S-model going on sale in May this year.